It is often necessary to determine the area under a curve or a portion of a curve drawn by a chart recording instrument. An example of such usage is found in gas or liquid chromatography, where the chart recorder shows a series of curves, each representing a component of the sample. The area under each peak is a measure of the quantity present of the coresponding elutent from the chromatograph column.
Several methods can be used to measure the area under the curves including cutting out and weighing the curves drawn on paper or the use of a planimeter. Another method is to use an automatic integrator built into the chart recorder. One such device employs a computing mechanism of the type called a ball and disc integrator. This device is arranged so that it causes an auxiliary pen to trace a zig-zag or triangular wave along the lower edge portion of the chart. The spatial frequency of this wave is proportional to the area under the main curve. Other devices use a voltage to frequency converter to drive an auxiliary pen. The pen traces a zig-zag line similar to the ball and disc integrator. The number of zig-zag lines under the corresponding curve correspond to the area under the curve.
The present invention teaches an improved integrator that can be used with any standard single pen laboratory chart recorder. Unlike previous designs no modification is required to the recorder. The improved integrator has increased ease of readout and lower cost.